Dual-function plasma and non-ionising microwave coagulating electrosurgical instrument and electrosurgical apparatus incorporating the same

ABSTRACT

An electrosurgical device that is capable of both generating a plasma to perform surface coagulation and emitting a non-ionising microwave field (in the absence of plasma) to perform coagulation at a deeper level. The device comprises a probe tip that is connected to receive radiofrequency (RF) and/or microwave frequency energy from a generator, and also defines a flow path for a gas. The probe tip is adjustable between a first configuration, in which it defines a bipolar (e.g. coaxial) structure to produce a high electric field from the received RF and/or microwave frequency energy across the flow path for the gas to strike and sustain plasma and a second configuration, in which it defines an antenna structure to emit non-ionising microwave energy into tissue.

CROSS-REFERENCE TO RELATED APPLICATION

This application is a Divisional of U.S. patent application Ser. No.14/890,426, filed Nov. 10, 2015, now U.S. Pat. No. 10,342,595, which isa National Stage entry of International Application No.PCT/GB2014/051468, filed May 13, 2014, which claims priority to UnitedKingdom Patent Application No. 1308558.4, filed May 13, 2013. Thedisclosures of the priority applications are incorporated in theirentirety herein by reference.

FIELD OF THE INVENTION

The invention relates to electrosurgical apparatus in whichradiofrequency and/or microwave frequency energy is used to treatbiological tissue by causing hemostasis (i.e. sealing broken bloodvessels by promoting blood coagulation). In particular, the inventionrelates to surgical apparatus in which the radiofrequency (RF) and/ormicrowave energy is used in conjunction with a flow of gas to strike andsustain a thermal plasma.

BACKGROUND TO THE INVENTION

Argon plasma coagulation (APC) or argon beam coagulation (ABC) is aknown surgical technique for controlling surface bleeding in a mannerthat does not require physical contact between a surgical probedelivering the plasma and the lesion. APC can be performedendoscopically, whereby a jet of argon gas is directed through a probepassed through an endoscope. Ionization of the argon gas as it isemitted creates the plasma that causes coagulation.

To strike plasma it is desirable to have a high electric field (e.g.high voltage or high impedance condition). Accordingly, it is necessaryto set-up a high impedance state in order to enable the high voltage(high electric field) necessary to break down the gas to generateplasma. In one embodiment discussed in WO 2009/060213, a high voltage(high impedance) condition is set up using a flyback circuit that uses alow frequency (e.g. radiofrequency) oscillator circuit and a transformerwhose primary winding is connected to the low frequency oscillatorcircuit by a suitable driver and switching device (e.g. gate drive chipand a power MOSFET or BJT). The arrangement generates high voltagepulses or spikes which strike or otherwise initiate the plasma. Oncestruck, the plasma may be maintained by a supply of microwave energy.

SUMMARY OF THE INVENTION

At its most general, the present invention provides an electrosurgicaldevice that is capable of both generating a plasma to perform surfacecoagulation and emitting a non-ionising microwave field (in the absenceof plasma) to perform coagulation at a deeper level. The formerfunctionality may be useful in the same way as the conventional APCtechnique, e.g. for treating surface bleeding. The latter functionalitymay be used to treat peptic ulcers or coagulate large blood vessels.

To achieve the dual functionality expressed above, the electrosurgicaldevice of the invention comprises a probe tip that is adjustable betweentwo configurations. The probe tip is connected to receive radiofrequency(RF) and/or microwave frequency energy from a generator, and alsodefines a flow path for a gas. In a first configuration, the probe tipdefines a bipolar (e.g. coaxial) structure to produce a high electricfield from the received RF and/or microwave frequency energy across theflow path for the gas to strike and sustain plasma. In a secondconfiguration, the probe tip defines an antenna structure to emitnon-ionising microwave energy into tissue. The antenna structure may bea radiating monopole antenna, which may take the form of a cylinder, aball, a stiff wire or a helix or a turnstile antenna that is capable ofemitting outwardly (i.e. away from the probe) an electric field from thereceived microwave frequency energy. Thus, in the first configurationthe device may use one or both of RF energy and microwave energy,whereas in the second configuration, the device preferably usesmicrowave energy.

The bipolar structure may comprise inner and outer conductors. The outerconductor may be retractable relative to the inner conductor to adjustthe probe tip between the first configuration and second configuration.For example, where the inner conductor and outer conductor are arrangedcoaxially, the outer conductor may retract from a first position(corresponding to the first configuration) where it surrounds the innerconductor, to a second position (corresponding to the secondconfiguration) where it is axially displaced rearwards (i.e. towards theproximal end of the device) to expose the inner conductor.

In the first configuration, the plasma may be struck using RF ormicrowave energy. Microwave energy may be used to sustain the plasmaafter it is struck. This arrangement may offer an advantage over RFplasma used in conventional electrosurgical systems, where the electricfield may collapse due to the capacitance of the cable and loadingcaused by tissue variations.

The impedance of the plasma is preferably matched to the impedance ofthe applicator (and energy delivery system) at the frequency of themicrowave energy to enable efficient transfer of the microwave energy,produced by the microwave source, into the plasma. Where microwaveenergy is used, the applicator and/or generator may be tuned (staticallyor dynamically) to ensure that the plasma is matched into the loadpresented by the tissue. At microwave frequencies, the cable forms adistributed element transmission line, where the impedance match betweenapplicator and energy source is determined by the source impedance ofthe microwave generator, the characteristic impedance of the cable(transmission line), the impedance of the applicator structure itselfand the impedance of the tissue. If the characteristic impedance of thecable is the same as the output impedance of the source then all of themicrowave power will be delivered into the applicator, less theattenuation caused by the cable (dielectric and conductor losses). Ifthe impedance of the applicator and the tissue is the same as thecharacteristic impedance of the cable, then the maximum power availableat the source will be transferred into the plasma/tissue load.Adjustments may be made to applicator structure in order to maintain thebest impedance match between the applicator and the plasma/tissue load,as explained below. Adjustments may also be made at the generator or atthe interface between the distal end of the first cable and the proximalend of the second (instrument) cable. These adjustments may be in theform of a change of capacitance and/or inductance of a matching network,i.e. stub tuning.

In this specification “microwave frequency” may be used broadly toindicate a frequency range of 400 MHz to 100 GHz, but preferably therange 1 GHz to 60 GHz. Specific frequencies that have been consideredare: 915 MHz, 2.45 GHz, 3.3 GHz, 5.8 GHz, 10 GHz, 14.5 GHz and 24 GHz.In contrast, this specification uses “radiofrequency” or “RF” toindicate a frequency range that is at least three orders of magnitudelower, e.g. up to 300 MHz, preferably 10 kHz to 1 MHz.

According to one aspect of the invention, there is provided anelectrosurgical instrument comprising: an elongate probe comprising acoaxial cable for conveying radiofrequency (RF) and/or microwavefrequency electromagnetic (EM) energy, and a probe tip connected at thedistal end of the coaxial cable for receiving the RF and/or microwaveenergy; and a gas passage for conveying gas through the elongate probeto the probe tip, wherein the coaxial cable comprises an innerconductor, an outer conductor and a dielectric material separating theinner conductor from the outer conductor, wherein the probe tipcomprising a first electrode connected to the inner conductor of thecoaxial cable and a second electrode connected to the outer conductor ofthe coaxial cable, and wherein the first electrode and second electrodeare movable relative to each other between: a first configuration inwhich they are arranged to produce an electric field from the receivedRF and/or microwave frequency EM energy across a flow path of gasreceived from the gas passage to produce a thermal or non-thermalplasma, and a second configuration in which the first electrode extendsdistally beyond the second electrode to form a radiating structure foremitting a microwave EM field outwardly from the probe tip. Thus, in thefirst configuration the instrument may operate to produce a plasmasuitable for surface (or superficial) coagulation of biological tissueand/or sterilisation/disinfection of biological tissue or instruments.The gas may be argon, or any other suitable gas, e.g. carbon dioxide,helium, nitrogen, a mixture of air and any one of these gases, i.e. 10%air/90% helium. The high electric field for striking the plasma may becaused by creating a high impedance condition for either the RF EMenergy or the microwave EM energy at the probe tip. This can be achievedthrough the selection of a suitable geometry for the first and secondelectrodes. For example, a piece of insulating dielectric material, suchas quartz or other similarly low loss material, may be located betweenthe first and second electrodes in the first configuration. This mayincrease the impedance and therefore facilitate the creation of a highelectric field. In the first configuration, the second electrode may bearranged to extend past (e.g. more distally than) the first conductor toensure that non-ionising radiation is not emitted.

In the second configuration, the probe can radiate microwave frequencyenergy in the form of a microwave EM field for deeper coagulation ofbiological tissue or sterilisation.

In a preferred embodiment, the instrument is capable of receiving bothRF and microwave EM energy. The RF EM energy may be for striking theplasma, and may be received as a high voltage pulse. The microwave EMenergy is for sustaining the plasma, i.e. delivering power into theplasma to maintain the state of ionisation. This may also be received asa pulse. The plasma may be struck repeatedly in a manner to produce aquasi-continuous beam of plasma. The advantage of this arrangement overconventional APC device which use only RF EM energy is that the plasmawill not collapse due to capacitive loading or changing from a dry towet environment. Moreover, the dual configuration nature of theinstrument enables it to switch to a state suitable for deepcoagulation, where the second electrode (and the insulating dielectricmaterial) are withdrawn to a distance where the first electrode isexposed such that is acts as a radiating microwave monopole antennastructure as discussed below.

It may also be possible to strike the plasma using the microwavefrequency energy, e.g. by using a microwave resonator or an impedancetransformer, i.e. a quarter wave transformer that transforms a lowvoltage to a higher voltage to strike plasma using a higher impedancetransmission line that is a quarter wave (or an odd multiple thereof)long at the frequency of operation. This high impedance line may beswitched in to strike plasma and switched out (i.e. to return to a lowerimpedance line) once the plasma has been struck and it is required tosustain plasma. A power PIN or varactor diode may be preferably used toswitch between the two states, although it may be possible to use aco-axial or waveguide switch.

The elongate probe may comprise a sleeve surrounding the coaxial cable.The sleeve may act to protect the coaxial cable, but may also define thegas passage, e.g. as a space between an inside surface of the sleeve andan outside surface of the coaxial cable. The gas passage may have aninput port located at a proximal end of the sleeve for connecting to asource of gas (e.g. a pressurised gas canister or the like).

The sleeve may further be the means for causing relative movementbetween the first and second electrodes. Relative movement between thefirst and second electrodes may be achieved by sliding a conductive(e.g. metallic) catheter over a microwave co-axial cable, whose outerconductor may also metallic. In this configuration the inner surface ofthe catheter (or tube that slides over the co-axial cable) must makegood electrical contact with the outer conductor of the coaxial cable.This may be achieved by providing a gas permeable conductive structurethat is slidable relative to the second electrode or outer electrode ofthe coaxial cable and permits gas to flow through it. The gas permeableconductive structure may be any one of: a conductive mesh; a cage ofradially extending conductive wires or springs; and a plurality ofcircumferentially spaced radially protruding dents. The gas permeableconductive structure may thus provide a plurality of (e.g. four or more)circumferential connections or point contacts will need to be made toensure that a good electrical connection is made for the microwavesignal. This solution may provide a balance between having enoughconnection points to create an appropriate environment for the microwaveenergy to propagate, to allow enough gas to flow and allow the outercatheter to be moved over the co-axial cable with relative ease.

In one embodiment, the second electrode may be mounted on or formed atthe distal end of the sleeve, and the sleeve may be retractable relativeto the coaxial cable. In other words, the sleeve may be capable of beingdrawn back to reveal the first electrode at the probe tip. The sleevemay be coaxial with the coaxial cable. The first and second electrodesmay thus be coaxial with each other in the first configuration. Thesecond electrode may be an annular band of conductive material on thedistal end of the sleeve. The dielectric material mentioned above may bea quartz collar mounted on the sleeve inwardly of the annular band.Alternatively or additionally, the dielectric material may be part ofthe inner electrode, as discussed below.

The retracting sleeve may comprise two or more telescoping sections. Thetelescoping sections may have a fluid tight seal therebetween to preventthe gas from escaping. The slidable outer sleeve may be retracted orextended using a mechanical or electromechanical system, i.e. amechanical slider, a linear motor or a stepper motor arrangement. Asexplained below, the position of the outer sleeve with respect to theouter conductor of the co-axial cable may be determined by a return lossor impedance match/mismatch measurement made using a reflected power orforward and reflected power measurement, i.e. a reflectometer or VSWRbridge measurement, using a detector(s) within the generator or withinthe probe.

In an alternative embodiment, the coaxial cable itself may be movablewithin the sleeve. In this arrangement the sleeve may be secured, e.g.fixed, to a proximal handpiece, which may include a manual slider or anyof the movement mechanisms mentioned herein for sliding the coaxialcable within the sleeve.

The first electrode may be a radiating microwave monopole antennastructure coupled to receive RF and/or microwave EM energy from thecoaxial cable. The outer conductor of the coaxial cable may be groundedto form an unbalanced feed or may be floating to form a balanced feed tothe antenna, i.e. where the voltage on both conductors is going up anddown. Preferably the first electrode is shaped to act as a microwaveantenna for emitting a microwave field corresponding to the receivedmicrowave EM radiation. For example, the monopolar radiating structuremay comprise a cylinder of dielectric material having a hemisphericaldistal end surrounding a length of the inner conductor of the coaxialcable which protrudes beyond the outer conductor and extends through thecylinder of dielectric material to protrude at its hemispherical distalend. Other distal end shapes are possible, e.g. ball or flat end. Thecylinder may be made of low loss ceramic material. The presence of thedielectric cylinder can improve the energy delivery into tissue, e.g. byreducing the amount of reflected power. The end of the length of innerconductor that protrudes from the hemispherical distal end of thecylinder may be rounded, e.g. shaped into a hemisphere, to provide amore uniform emitted field.

Preferably the monopolar radiating structure (i.e. the first electrodein the second configuration) is arranged to be well matched to theimpedance of blood at the frequency of the microwave EM radiation toproduce non-ionising radiation that is efficiently coupled into blood tocause controlled coagulation.

The outer electrode of the coaxial cable may be connected to the secondelectrode by a conductive mesh that permits gas to flow through it. Theconductive mesh may therefore be mounted in the passage in the probe,i.e. in the space between the coaxial cable and the sleeve.Alternatively, the space between the coaxial cable and the sleeve may bedivided into a plurality of sub-passages, e.g. by divider elementsconnected to or part of the sleeve. In this situation, the dividerelements or a separate connector element may provide an electricalconnection between the outer conductor of the coaxial cable and thesecond electrode. The connection may also be made by one flexible wireor strip, which may be soldered or crimped to the second electrode.

The probe may be used laporascopically or may be dimensioned to beinsertable through a scoping device, e.g. through the instrument channelof an endoscope, gastroscope, bronchoscope or the like. For example, thecoaxial cable may have a diameter of 2.5 mm or less, preferably 2.2 mmor less. The sleeve may have an outer diameter less than 2.6 mm,preferably less than 2.5 mm. For larger laparoscopic instruments, theouter diameter may be 3 mm or more, and larger diameter co-axial cablemay be used.

According to another aspect of the invention, there is providedelectrosurgical apparatus for performing coagulation comprising: amicrowave signal generator for generating microwave EM energy; anelectrosurgical instrument as described above connected to receive themicrowave EM energy; a feed structure for conveying the microwave EMenergy to the probe, the feed structure comprising a microwave channelfor connecting the probe to the microwave signal generator, a gas feedconnected to supply gas to electrosurgical instrument, wherein theapparatus is operable: in a surface coagulation mode when theelectrosurgical instrument is in the first configuration and gas issupplied thereto, whereby the microwave EM energy delivered to the probetip is arranged to strike and/or sustain a gas plasma between the firstand second electrodes; and in a deep tissue coagulation mode when theelectrosurgical instrument is in the second configuration without gassupplied to thereto, whereby the microwave EM energy delivered to theprobe tip is arranged to emit a non-ionising electric field outwardlyfrom the probe tip. The apparatus may include a radiofrequency (RF)signal generator for generating RF electromagnetic (EM) energy having afirst frequency, wherein: the microwave frequency EM energy has a secondfrequency that is higher than the first frequency, the feed structureincludes an RF channel for connecting the probe to the RF signalgenerator, and in the surface coagulation mode, the apparatus isarranged to deliver the RF EM energy to the probe tip to strike the gasplasma between the first and second electrodes.

The apparatus may comprise a strike signal generation circuit arrangedto cause a pulse (or pulses) of RF EM radiation to be delivered to theprobe to generate the high electric field across the flow path forstriking the plasma, wherein the strike signal generation circuitincludes control circuitry arranged to use a detectable characteristicof a pulse of microwave EM radiation on the microwave channel to triggergeneration of the pulse of RF EM radiation. The RF EM radiation is thusused to strike the plasma, whereas the microwave EM radiation is used tosustain the plasma. By coordinating the delivery of an RF strike pulsewith a pulse of microwave EM radiation as described above, the apparatusis capable of striking the plasma with greater certainty.

The apparatus may further comprise a microwave signal detector forsampling forward and reflected power on the microwave channel andgenerating therefrom a microwave detection signal indicative of themicrowave power delivered by the probe; and a controller incommunication with the microwave signal detector to receive themicrowave detection signal, wherein the controller is operable to selectan energy delivery profile for the microwave EM radiation, the energydelivery profile for the microwave EM radiation being for coagulation oftissue, wherein the controller comprises a digital microprocessorprogrammed to output a microwave control signal for the microwave signalgenerator, the microwave control signal being for setting the energydelivery profile for the microwave EM radiation, and wherein thecontroller is arranged to determine a state for the microwave controlsignal based on the received microwave detection signal. The arrangementmay be used to measure the reflected microwave signal, whereby themicrowave detection signal is representative of whether or not a plasmahas been struck. The signal detector may also be arranged tocontinuously monitor the forward and reflected microwave EM radiation toensure that the best impedance match is maintained during plasmadelivery. The microwave signal detector may comprise forward andreflected signal detectors (e.g. suitable directional power couplers onthe microwave channel). The detectors may be arranged to detect signalmagnitude only, e.g. they may be diode detectors. Alternatively, thedetectors may be arranged to detect magnitude and phase, e.g. they maybe heterodyne detectors. The microwave detection signal may thus berepresentative of return loss or impedance match information. Therelative position of the first and second electrodes of theelectrosurgical instrument may be adjustable by the controller in thesurface coagulation mode (i.e. when plasma is being generated) until aset return loss threshold is reached, i.e. 8 dB, 10 dB or 12 dB.

The apparatus may include a movement mechanism for causing relativemovement between the first electrode and second electrode, wherein thecontroller is arranged to communicate a control signal to the movementmechanism based on the received microwave detection signal. The movementmechanism may be mechanical, and may be manually controlled, e.g. by theoperator of the instrument. The movement mechanism may comprise anactuator, e.g. lever or pull arm, located at the distal end of theinstrument, e.g. a sliding or rotating mechanism that is moved by hand.

However, it is also contemplated herein to control the relative movementof the first and second electrode (i.e. setting the first and secondconfigurations) in an automated manner, e.g. using an electromechanicalmechanism. For example, in one embodiment, there may be a configurationcontroller arranged to automatically move the sleeve and operate the gassupply in accordance with the rate of blood flow at the treatment site.This feature may be used to ensure that large bleeds are dealt with inan expedient manner and that the depth of heating of healthy tissue islimited.

Furthermore, the controller may be arranged to automatically operate themovement mechanism as a means for controlling the impedance match intothe plasma. Reflected and forward power measurements on the microwavechannel may be used to control the position of the outer catheter withrespect to the inner co-axial cable (or the inner electrode attached tothe co-axial cable) by hand movement or by means of an electromechanicalactuator (PZT actuator, a magnetostrictive actuator, stepper motor,linear motor) based on return loss measurements or impedance match. Theoccurrence of a deep or heavy bleed whilst performing ABC or surfacecoagulation may cause the plasma to be extinguished, which in turn wouldlead to the return loss measurement changing, i.e. from 10 dB (goodmatch) to 2 dB (poor match). In the present invention, the outer sleevemay be automatically moved back to allow the microwave antenna to bedeployed to enable non-ionising microwave energy to be coupled into theblood or vessel instead of ionising gas (plasma) to produce deepercoagulation to deal with the larger bleeder.

The configuration controller may include a stepper motor or linear motorconnected to the sleeve or the coaxial cable to move the first andsecond electrodes relative to one another. The movement of the firstelectrode may also be based on a flow rate measurement instead of or aswell as the impedance match or return loss measurement. In thisinstance, the mode of operation is automatically changed from surfacecoagulation (ABC) to deeper coagulation (extended monopole antenna todeliver non-ionising microwave radiation) to produce deep coagulationbased on an increase in the rate of blood flow.

The configuration controller may be connected to a valve to control thegas supply, e.g. to switch off the supply when the instrument moves tothe second configuration and to switch it on when the instrument movesto the first configuration. The valve may be part of the instrument,e.g. integrated between the sleeve and the coaxial cable, or it may belocated outside the instrument, e.g. in the gas feed.

Moreover, in combination with the microwave signal detector mentionedabove, the configuration controller may be arranged to control theposition of the sleeve in the first configuration when the plasma ispresent on the basis of the microwave detection signal to minimise thereflected microwave signal. In other words, the configuration controllercomprises a feedback arrangement for fine tuning the position of thesleeve in the first configuration to facilitate efficient delivery ofthe plasma.

While the instrument may be arranged to generate a thermal plasma whenin the first configuration, it may also be arranged to generate anon-thermal plasma for sterilisation. With a co-axial applicatorstructure that has a plasma generating region with a diameter of between3 mm and 5 mm, i.e. the inner diameter of the outer conductor within theco-axial structure has a diameter of between 3 mm and 5 mm, and a quartztube that fits tightly inside with a wall thickness of between 0.25 mmand 1 mm, and where the outer diameter of the inner conductor is between0.75 mm and 4 mm (allowing a space for gas to flow in the region betweenthe inner conductor and the inner wall of the quartz tube), that anon-thermal plasma suitable for disinfection or sterilisation can beproduced by operating the generator in pulsed mode with a duty cycle ofless than 40%, i.e. 28%. In one embodiment, the rms power in a singlemicrowave pulse is 50 W and the pulse ON time is 40 ms, within a totalperiod of 140 ms, i.e. the average power delivered into the plasma is14.28 W at 2.45 GHz. When an RF strike pulse is used in thisconfiguration, the duration of the RF strike pulse is around 1 ms, andthe frequency of the sinusoidal oscillations was 100 kHz. The amplitudewas around 1 kV peak (707 Vrms). The RF power was less than 10% of themicrowave power. The RF pulse was synchronised to the microwave burst orpulse and triggered on the rising edge of the microwave burst or pulse.

To produce thermal plasma, the duty cycle may be increased, i.e. to 50%or continuous wave (CW) and/or the rms power level may be increased,i.e. to 75 W or 100 W for this particular applicator geometry (if thegeometry decreased or increased then the microwave power and theamplitude of the RF strike pulse would be adjusted accordingly). Theratio of RF to microwave power will preferably remain constant, i.e.less than 10% for non-thermal and thermal plasma.

Having the ability to perform sterilisation at the distal end of theinstrument may be particularly advantageous for the purpose disinfectingthe instrument channel of scopes. In order words, the non-thermal plasmais emitting as the instrument is withdrawn from the scope (e.g.endoscope or the like) to treat the inner surface of the instrument.Whilst non-thermal plasma is preferred for this process, it may also bepossible to achieve sterilisation by delivering non-ionising microwaveRF radiation only, i.e. in the absence of gas.

The sterilising function of the non-thermal plasma may also be used tosterilise body cavities before or after treatment. Where the device isused to clean or sterilise instruments, e.g. endoscopes or gastroscopes,the device may be configured to produce a combination of non-thermalplasma and non-ionising microwave radiation. The device may also beconfigured to produce non-thermal plasma, thermal plasma andnon-ionising microwave radiation where it is used in NOTES procedures orwhere it is advantageous to be able to perform surface coagulation,sterilisation of body tissue and deep coagulation of large vessels orbleeders.

The apparatus and instrument may thus have four use modes:

-   -   non-thermal plasma used to sterilise or disinfect the instrument        channel of an endoscope or any other scope or other equipment or        to sterilise or disinfect biological tissue or external surfaces    -   non-ionising microwave radiation to sterilise or disinfect the        instrument channel of endoscopes, other scopes or other        equipment    -   thermal plasma for surface or superficial coagulation    -   non-ionising microwave radiation for deeper coagulation.

In other words, the sleeve of the instrument may be adjustable betweenfour states:

-   -   Non-ionising microwave radiation: monopole radiating antenna        exposed to emit non-ionising microwave radiation for deep        coagulation;    -   Plasma strike using RF and microwave energy: the radiating        monopole is covered by outer sleeve and gas is introduced into        the region so that plasma (thermal for surface coagulation        and/or non-thermal for sterilisation/disinfection) can be struck        and sustained;    -   Plasma strike using microwave energy only: the proximity between        the inner and outer conductors is adjusted to generate a high        enough E-field to strike plasma;    -   Plasma sustain using the microwave field only: the proximity        between the inner and outer conductors is adjusted to generate a        low impedance environment to allow plasma to be sustained.

The sleeve may have a plurality of predetermined set positionscorresponding to each configuration. The instrument may include amechanism for retaining the sleeve in each one of the set positions,e.g. a locating groove or ratchet mechanism.

The instrument may thus provide four functions: sterilisation usingnon-thermal plasma, surface tissue coagulation using thermal plasma,deep tissue coagulation using non-ionising microwave radiation andsterilisation using non-ionising microwave radiation. It may beappreciated that having a single instrument capable of performing two orthree or four functions as described above enables rapid and efficienttreatment because the instrument does not need to be withdrawn if adifferent function is required.

The RF and microwave EM energy may be delivered separately orsimultaneously in any of the use modes of the apparatus. For example,only RF EM energy may be used to strike and sustain the plasma in thesurface coagulation mode, and only microwave EM energy may be used onlyto deliver non-ionising radiation in the deep coagulation mode.Alternatively, a high voltage RF electric field may be created to strikethe plasma, followed by a microwave frequency field augmented with a RFfield to sustain plasma.

Similarly, the microwave frequency EM energy may be used to augment theRF strike voltage to help guarantee a plasma strike. This may be done bycontrolling the microwave signal generator to produce peak power for theduration of the RF strike pulse, and then produce a reduced power levelto sustain plasma after it has been struck.

In another aspect, the present invention may provide an instrumentsuited for performing APC where the plasma is struck by a pulse of RFenergy and sustained by a pulse of microwave frequency energy. Accordingto this aspect, there may be provided an electrosurgical instrumentcomprising: an elongate probe comprising a coaxial cable for conveyingradiofrequency (RF) and microwave frequency electromagnetic (EM)radiation, and a probe tip connected at the distal end of the coaxialcable for receiving the RF and microwave radiation separately orsimultaneously from the coaxial cable; and a gas passage for conveyinggas through the elongate probe to the probe tip, wherein the coaxialcable comprises an inner conductor, an outer conductor and a dielectricmaterial separating the inner conductor from the outer conductor,wherein the probe tip comprising a first electrode connected to theinner conductor of the coaxial cable and a second electrode connected tothe outer conductor of the coaxial cable, and wherein the firstelectrode and second electrode are arranged to produce a high electricfield from the received RF EM energy across a flow path of gas receivedfrom the gas passage in order to strike a plasma, and arranged todeliver the received microwave energy to sustain the plasma after it isstruck.

This device may not have the dual functionality discussed above, butinstead utilises microwave frequency energy to improve on existing APCsystems. The advantage of using combined RF and microwave frequencyenergy to create the plasma beam is that the energy required to strikethe plasma does not rely on an external return path and the energy tosustain the plasma can be accurately controlled to ensure rapid andefficient treatment. Alternatively, the plasma may be generated usingthe RF only, as is conventional, and the microwave energy may beprovided only in order to provide the additional function of deep tissuecoagulation or sterilisation in the scope instrument channel cleaningapplication or sterilisation of biological tissue in the NOTES ornatural orifice application.

As with the dual functionality aspect discussed above, the plasma may begenerated at the distal end of a flexible microwave cable with adiameter of less than 2.5 mm, which enables the instrument to beintroduced down the instrument channel of any scoping device, i.e.endoscope, gastroscope, etc. It may also be used to clean or disinfectthe instrument channel of endoscopes and be used to disinfect tissuebefore or after the treatment of ulcers, and/or to kill or reducebacteria manifested in natural orifices of the body and/or to sterilisewound beds before skin grafts are performed and/or disinfect skin beforeit is grafted onto the body.

It may also be used in ear, nose and throat (ENT), in endometriosesprocedures and general open procedures where it is necessary to preventor stem blood flow/loss.

The present invention can be used in a number of open and endoscopicsurgical applications where surface coagulation is beneficial, i.e. tostop superficial bleeding on the liver bed or breast flap surgery, totreat surface ulcers, etc. It may be particular useful in proceduresthat minimise bleeding in the upper and lower gastrointestinal tract,and it may play a part in the treatment for variceal bleeding andbleeding from peptic and duodenal ulcers, diverticulosis,angiodysplasia, colitis, colon carcinoma and anorectal disease.

BRIEF DESCRIPTION OF THE DRAWINGS

Embodiments of the invention are discussed below with reference to theaccompanying drawings, in which:

FIG. 1 is a known power delivery system suitable for use with thepresent invention;

FIG. 2 is a schematic view of electrosurgical apparatus that is anembodiment of the invention;

FIG. 3A is a schematic cross-sectional view of an electrosurgicalinstrument that is an embodiment of the invention in a firstconfiguration;

FIG. 3B is a schematic cross-sectional view of the electrosurgicalinstrument that of FIG. 3A in a second configuration;

FIG. 4A is a schematic cross-sectional view of an electrosurgicalinstrument that is an embodiment of the invention in a firstconfiguration;

FIG. 4B is a transverse cross-section taken along the line B-B in FIG.4A;

FIG. 4C is a schematic cross-sectional view of the electrosurgicalinstrument that of FIG. 4A in a second configuration;

FIG. 5 is a perspective view of the dielectric cylinder used to modelthe first electrode of an electrosurgical instrument that is anembodiment of the invention;

FIGS. 6A and 6B are microwave field simulations of the first electrodeshown in FIG. 5 with power delivered into representative models of bloodand liver tissue;

FIG. 6C is a microwave field simulation of the first electrode shown inFIG. 5 with a rounded inner conductor termination into the liver model;

FIGS. 7A and 7B are plots showing simulated return loss for thestructures of FIGS. 6A and 6C into representative models of blood andliver tissue respectively;

FIGS. 8A and 8B are microwave field simulations of another firstelectrode into representative models of blood and liver tissue;

FIGS. 9A and 9B are plots showing simulated return loss for thestructures of FIGS. 8A and 8B into representative models of blood andliver tissue respectively;

FIG. 10 is a microwave field simulation of another first electrode intoblood and liver tissue;

FIGS. 11A and 11B are plots showing simulated return loss for thestructure of FIG. 10 into representative models of blood and livertissue respectively;

FIGS. 12A and 12B are schematic cross-sectional views of anelectrosurgical instrument that is yet another embodiment of theinvention;

FIG. 13 is a perspective view of a handpiece suitable for operating theelectrosurgical instrument of the invention; and

FIG. 14 is a schematic cross-section view through the handpiece shown inFIG. 13.

DETAILED DESCRIPTION; FURTHER OPTIONS AND PREFERENCES

FIG. 1 shows a schematic diagram of a power delivery system 100disclosed in WO 2012/076844, which is suitable for use in the presentinvention.

The system 100 comprises an RF line-up 102 and a microwave line-up 104,which form parts of a RF channel and a microwave channel respectively.

The RF line-up 102 contains components for generating and controlling anRF frequency electromagnetic signal at a power level suitable forstriking a plasma, as described below. In this embodiment, it includesan RF oscillator 1001, a power controller 1002, an amplifier unit (herecomprising a driver amplifier 1003 and a power amplifier 1004), atransformer 1005 and an RF signal detector 1006.

The microwave line-up 104 contains components for generating andcontrolling a microwave frequency electromagnetic signal at a powerlevel suitable for treating biological tissue. In this embodiment itincludes a phase locked oscillator 1007, a signal amplifier 1008, anadjustable signal attenuator (e.g. an analogue or digital PIN diodebased attenuator attenuator) 1009, an amplifier unit (here a driveramplifier 1010 and a power amplifier 1011), a forward power coupler1012, a circulator 1013 and a reflected power coupler 1014. Thecirculator 1013 isolates the forward signal from the reflected signal toreduce the unwanted signal components present at the couplers 1012,1014, i.e. it increases the directivity of the couplers. The circulatoralso protects the transistors within the high power output stage, e.g.the power GaN or GaAs transistors. It is preferable for the isolationbetween ports 1 to 3, 2 to 1 and 3 to 2 to be as high as possible, i.e.greater than 15 dB, or more preferably more than 20 dB.

The RF line-up 102 and microwave line-up 104 are in communication with acontroller 106, which may comprise signal conditioning and generalinterface circuits 108, a microcontroller 110, and watchdog 1015. Thewatchdog 1015 may monitor a range of potential error conditions, whichcould result in the system not performing to its intended specification,i.e. the system delivers the wrong dosage of energy into patient tissuedue to the output or the treatment time being greater than that demandedby the user. The watchdog 1015 comprises a microprocessor that isindependent of the microcontroller 110 to ensure that microcontroller isfunctioning correctly. The watchdog 1015 may, for example, monitor thevoltage levels from DC power supplies or the timing of pulses determinedby the microcontroller 110. The controller 106 is arranged tocommunicate control signals to the components in the RF line-up 102 andmicrowave line-up 104. In this embodiment, the microprocessor 110 isprogrammed to output an RF control signal C_(RF) and a microwave controlsignal C_(M) for the power controller 1002 and the adjustable signalattenuator 1009 respectively. These control signals are used to set theenergy delivery profile of the RF EM radiation and the microwave EMradiation output from the RF line-up 102 and microwave line-up 104respectively. In particular, the power controller 1002 and theadjustable signal attenuator 1009 are capable of controlling the powerlevel of the output radiation. Moreover, the power controller 1002 andthe adjustable signal attenuator 1009 may include switching circuitrycapable of setting the waveform (e.g. pulse width, duty cycle, andamplitude, etc.) of the output radiation.

The microprocessor 110 is programmed to output the RF control signalC_(RF) and the microwave control signal C_(M) based on signalinformation from the RF signal detector 1006 and forward and reflectedpower couplers 1012, 1014. The RF signal detector 1006 outputs a signalor signals S_(RF) which are indicative of the voltage and current (andoptionally the phase between the voltage and current) of the RF EMradiation on the RF channel. In this embodiment, the RF and microwavegenerator may be controlled by measurement of phase information only,which can be obtained from either the RF channel (from sampled currentand voltage information) or the microwave channel (from sampled forwardand reflected power information). The forward power coupler 1012 outputsa signal S_(M1) indicative of the forward power level and the reflectedpower coupler 1014 outputs a signal S_(M2) indicative of the reflectedpower level. The signals S_(RF), S_(M1), S_(M2) from the RF signaldetector 1006 and the forward and reflected power couplers 1012, 1014are communicated to the signal conditioning and general interfacecircuits 108, where they are adapted to a form suitable for passing tothe microprocessor 110.

A user interface 112, e.g. touch screen panel, keyboard, LED/LCDdisplay, membrane keypad, footswitch or the like, communicates with thecontroller 106 to provide information about treatment to the user (e.g.surgeon) and permit various aspects of treatment (e.g. the amount ofenergy delivered to the patient, or the profile of energy delivery) tobe manually selected or controlled, e.g. via suitable user commands. Theapparatus may be operated using a conventional footswitch 1016, which isalso connected to the controller 106.

The RF and microwave signals produced by the RF line-up 102 andmicrowave line-up 104 respectively are input to a signal combiner 114,which conveys the RF and microwave EM radiation separately orsimultaneously along a cable assembly 116 to the probe 118. In thisembodiment, the signal combiner 114 comprises a duplexer-diplexer unitthat allows energy at microwave and RF frequencies to be transmittedalong cable assembly 116 (e.g. a coaxial cable) to a probe (orapplicator) 118, from which it is delivered (e.g. radiated) into thebiological tissue of a patient into the instrument channel of a scope,e.g. an endoscope or another surface.

The signal combiner 114 also permits reflected energy, which returnsfrom the probe 118 along cable assembly 116, to pass into the microwaveand RF line-ups 102, 104, e.g. to be detected by the detectors containedtherein. As explained below, the apparatus may include a low pass filter146 on the RF channel and a high pass filter 166 on the microwavechannel, so that only a reflected RF signal enters the RF line-up 102and only a reflected microwave signal enters the microwave line-up 104.

Finally, the apparatus includes a power supply unit 1017 which receivespower from an external source 1018 (e.g. mains power) and transforms itinto DC power supply signals V₁-V₆ for the components in the apparatus.Thus, the user interface receives a power signal V₁, the microprocessor110 receives a power signal V₃, the RF line-up 102 receives a powersignal V₃, the microwave line-up receives a power signal V₄, the signalconditioning and general interface circuits 108 receives a power signalV₅, and the watchdog 1015 receives a power signal V₆.

FIG. 2 shows a schematic diagram of electrosurgical apparatus 200 thatis an embodiment of the invention. The apparatus 200 comprises anelectrosurgical instrument 202 capable of delivering plasma ornon-ionising electromagnetic (EM) radiation from its distal end.Examples of the structure of the instrument 202 are described below.

The instrument 202 is connected to a power delivery system, which may beas described with reference to FIG. 1. However, in the embodiment ofFIG. 2, the power delivery system comprises an radiofrequency (RF)radiation source 204 and a microwave radiation source 206 which areconnected to deliver power to the proximal end of the instrument 202 viaa feed structure 208. The feed structure 208 may include a signalcombiner unit 210 as discussed above. The RF source 204 and themicrowave source 206 may be arranged to output an RF signal and amicrowave signal respectively based on control signals C_(RF) and C_(M)from a controller (not shown).

The instrument 202 is also connected to receive a gas, e.g. from apressurised gas source 214 via supply line 212. A control valve 216 onthe supply line 212 may be arranged to control the flow of gas receivedby the instrument 202, e.g. based on a control signal C_(g) from thecontroller. It may be desirable to activate the gas control valve and/orflow controller prior to activating the RF and/or microwave energysources in order to ensure that gas is present when said energy sourcesare activated as it is necessary for gas to be present in the plasmaforming region before plasma can be generated. It may be preferable toinclude a gas sensor in the plasma forming region and the signals fromthis sensor used to control the gas flow valves. This system also helpscontrol gas utilisation and prevents the patient from filling up withargon (or other) gas.

The RF and microwave measurement information may also be used to controlthe gas controller, i.e. the gas control valve may be closed when RFand/or microwave power cannot be detected using voltage/current and/orforward/reflected power monitoring circuits within the generator. It maybe preferable to wait for a set period of time, i.e. 20 ms or 200 msbefore shutting off the gas supply. This arrangement acts as a safetyfeature and as a means of controlling gas usage.

FIGS. 3A and 3B shown a first embodiment of an electrosurgicalinstrument 300 according to the invention. The instrument 300 comprisesan elongate probe made up of a central coaxial cable 302 surrounded by atubular sleeve 304. The proximal end of the coaxial cable 302 (shown onthe left in FIGS. 3A and 3B) terminates at a suitable connector 306 thatis adapted to connect to the feed structure that supplied the RF andmicrowave signals. The coaxial cable 302 conveys the RF and microwavesignals to the distal end of the instrument (on the right in FIGS. 3Aand 3B).

The distal end of the coaxial cable 302 terminates at a insulatingelement 308 such as a glass bead or ceramic disc positioned between thebody of the coaxial cable and the cylindrical cap to prevent shorting orbreakdown from occurring. Alternatively, the dielectric within themicrowave cable may extended by e.g. 0.1 mm to 0.2 mm past the outerconductor of the co-axial cable. The outer conductor 310 of the coaxialcable stops at the insulating element 308, but the inner conductor 312continues through the insulating element 308 and protrudes beyond theinsulating element 308 for a length selected (using simulations) to givebest impedance match for deep coagulation. The protruding length issurrounded by a cylindrical ceramic (or other suitable dielectric ormagnetic material) cap 314, which terminates at its distal end in a dome316, e.g. a hemisphere. The inner conductor 312 protrudes slightly fromthe dome 316. The inner conductor 312 and cylindrical cap function as afirst electrode of the instrument.

The sleeve 304 is a arranged to slide in a longitudinal directionrelative to the coaxial cable 302. In this embodiment, the sleeve 304 isslidably mounted in a telescopic manner within a proximal base piece318. A pull wire (not shown) may extend through the connector 306 toassist positioning of the sleeve 304 relative to the coaxial cable. Thepull wire may be manually operated, or may be connected to an automatedcontrol mechanism, e.g. a stepper motor or linear motor, which canautomatically control the position of the sleeve 304, e.g. on the basisof a control signal from the controller.

The pull wire may also take the form of a rigid section of tubeconnected to the co-axial cable at one end and arranged to slide overthe sleeve (catheter). It may be preferable to introduce two cathetersections, a first section at the proximal end that is fixed to a ‘Y’section (used to introduce the microwave/RF energy my means of aco-axial cable and the gas by means of a tube). The two inputs to the‘Y’ piece and the common output must be sealed and be gas tight. A luerlock device with a circumferential seal that can be adjusted bytightening a thread may be used for this purpose. The first rigidsection may slide over a second less rigid section (the main catheter)that is introduced inside the instrument channel of an endoscope or acannula or the like. A seal is provided between the rigid proximalsection and the flexible section to ensure that gas cannot escape at theinterface between the two sections.

The sleeve 304 surrounds the coaxial cable 302 to define an annularspace 320 between the outer surface of the coaxial cable 302 and theinner surface of the sleeve 304. Radial support elements or spacers (notshown) may be used to locate the coaxial cable 302 within the sleeve.The annular space 320 may be used to transport gas to the distal end ofthe instrument. The base piece 318 has a port 322 in a side surfacethereof that is connected to the gas supply line. Gas tight seals 324,326, which may be O-rings or the like, are provided at the join betweenthe base piece 318 and the connector 306 and at the sliding junctionbetween the base piece and sleeve 304 in order to minimise the escape ofgas. Gas introduced into the port 322 therefore flows along the annularspace 320 to exit the instrument at its distal end.

The sleeve 304 has an electrically conductive inner surface 321 along alength thereof leading up to its distal end. This electricallyconductive inner surface 321 is electrically connected to the outerconductor 310 of the coaxial cable 302. In this embodiment, this is doneby means of an electrically conductive mesh 328 mounted within theannular space 320. The mesh is porous, and therefore permits the gas toflow through it whilst also providing an electrical connection. Thiscould also be achieved using a spring or a plurality of small wireselectrically connected, i.e. soldered or crimped or trapped, to one orboth surfaces of conductors or electrodes 310 and 321. Providing atleast two, ideally at least four, circumferential contact points aroundthe circumference of the conductor(s) can ensure good enough electricalcontact for the microwave energy to propagate unimpaired. It may also bepossible and preferable to put a plurality of dents or a partial crimp(e.g. 180°) in/on one of the conductors in order to make the necessaryelectrical contact needed whilst also enabling the gas to flow onto theplasma generating region or the distal end of the device where plasma isformed.

The electrically conductive inner surface 321 of the sleeve is furthercovered by an insulating tube 330 (e.g. made of quartz, ceramic or thelike) along a distal length thereof that can overlap longitudinally withthe cylindrical cap 314. The electrically conductive inner surface 321and insulating tube 330 function as a second electrode of theinstrument.

The slidable sleeve permits the instrument to adopt two configurations.In a first configuration, as shown in FIG. 3B, the electricallyconductive inner surface 321 of the sleeve 304 is longitudinally in linewith the cylindrical cap 314. This configuration sets up a region ofhigh impedance which exhibits a high electric field when the RF ormicrowave signal is supplied to the instrument. In this configuration,the instrument may be adapted to deliver plasma, e.g. thermal plasma forsurface coagulation or non-thermal plasma for sterilisation, from thedistal end of the probe.

The microprocessor may be arranged to output a control signal to adjustthe position of the sliding sleeve relative to the coaxial cable basedon the detected return loss or impedance mismatch that is determined inthe controller from the microwave detection signal. This control may bedone when plasma is being generated e.g. to maintain a pre-set requiredmatch or return loss, e.g. 10 dB (90% of the microwave energy isdelivered into the plasma).

In a preferred embodiment, the plasma (thermal or non-thermal asrequired) is generated by the follow steps:

-   -   supply gas to the distal region of the instrument (i.e. to the        region between the quartz tube 330 and cylindrical cap 314),    -   sending a pulse of RF energy through the coaxial cable to strike        a plasma in the gas at the distal region by generating a high        electric field in the region, and    -   sending a pulse of microwave energy through the coaxial cable to        sustain or maintain the plasma to ensure that appropriate        treatment takes place.

The RF pulse may be automatically triggered by a characteristic (e.g.the rising edge) of the microwave pulse, so that the strike and sustainpulses are always synchronised. The RF pulse is arranged to have avoltage suitable for setting up an electric field for striking theplasma. The voltage may be between 150 V and 1500 V peak, morepreferably between 250 V and 750 V peak. The frequency of the RF pulsesmay be between 100 kHz and 1 MHz, where a the window or burst ofsinusoidal waveform or signals is gated (based on the detected microwavepulse) and is preferably between 0.5 μs and 10 ms.

The delivered microwave power may be monitored (e.g. by measuringforward and reflected microwave signals) in order to check the status ofthe plasma.

In the embodiment above, the plasma is struck by the RF signal. In otherembodiments, the plasma may be struck by the microwave signal only,because the close proximity between the inner and outer conductorsenables a high electric field to be generated from the microwave signal.For example, if it is possible to deliver 25 W of CW microwave power tothe distal end of the instrument then this may create a high enoughelectric field. One possible means of striking plasma using themicrowave field is to decrease the distance between the two conductorswithin the plasma generating region at the time plasma is struck andthen increase the distance again once it has been struck in order tocreate the optimal environment (impedance) for plasma to be sustained.In this configuration, the adjustable sleeve (outer tube) may bearranged to be or set up to be in four possible positions, which are asfollows:

Position 1—monopole radiating antenna exposed to deliver non-ionisingmicrowave radiation for deep coagulation;

Position 2—Plasma generating region set up, radiating monopole iscovered by outer sleeve and gas is introduced into the region so thatplasma (thermal for surface coagulation and/or non-thermal forsterilisation/disinfection) can be struck and sustained using RF andmicrowave energy respectively;

Position 3—Plasma is struck using microwave energy and the proximitybetween the inner and outer conductors is adjusted generate a highenough E-field to strike plasma;

Position 4—Plasma is sustained using the microwave field and theproximity between the inner and outer conductors is adjusted generate alow impedance environment to allow plasma to be sustained.

The control of the position of the sleeve and the formation of thevarious regions may be carried out automatically based on movement of alinear actuator or a stepper motor based on voltage and/or currentsignals from the RF channel and/or forward and/or reflected powersignals from the microwave channel.

If the coaxial section that includes the insulating tube 330 andcylindrical cap 314 has an impedance of 50 ohms, then the peak voltagewill be 50 V, which produces an electric field of 50 kV/m if thedistance between the inner conductor 312 and the electrically conductiveinner surface of the sleeve 304 conductor is 1 mm. Such a field may becapable of striking a plasma if argon was present in the gap. It mayalso be possible to switch in an impedance transformer, i.e. a quarterwave transformer, to produce a the necessary voltage increase needed tostrike plasma, e.g. a quarter wave line with an impedance of 250Ω with a50Ω source impedance and a power source of 25 W, will produce a strikevoltage of:

$\sqrt{\left( {\frac{(250)^{2}}{50} \times 25} \right)} = {177\mspace{14mu}{V.}}$

In such embodiments, the instrument may only receive a microwave input;the power delivery system need not have an RF source in thisarrangement.

In a second configuration, as shown in FIG. 3A, the sleeve 304 is slidback relative to the coaxial cable 302 to expose a length of thecylindrical cap 314 at the distal end of the device. The exposed endfunctions as a radiating monopole microwave antenna. In thisconfiguration, a microwave signal is supplied to the coaxial cable inthe absence of gas. The microwave signal is emitted at a non-ionisingradiation field to perform deep tissue coagulation. The levels ofnon-ionising microwave power delivered at the distal radiating monopolemay be between 2.5 W and 50 W continuous wave power; the level isdependent on the rate of blood flow or the size of the vessel beingcoagulated. The power level also depends on the properties of themicrowave transmission cable used to deliver the microwave energy fromthe generator to the applicator or antenna.

FIGS. 4A, 4B and 4C show a second embodiment of an electrosurgicalinstrument 400 according to the invention. Common features with FIGS. 3Aand 3B are given the same reference numbers. The second embodiment issimilar to the first embodiment except for the way in which the outerconductor 310 of the coaxial cable 302 is electrically connected to theelectrically conductive inner surface 321 of the sleeve 304. Instead ofconductive mesh, the second embodiment using a split conical member 402made of electrically conductive material to connect the outer conductor310 of the coaxial cable 302 to the electrically conductive innersurface 321 of the sleeve 304. The conical member 402 comprises aplurality of fingers which flare out from the coaxial cable towards thesleeve 304. The sleeve 304 may slide relative to the fingers, or theconical member 402 may be fixed to the sleeve and slide over the coaxialcable.

FIG. 4B shows a cross-sectional view through the split conical member402, which shows how the gas can pass between the fingers to reach thedistal end of the probe.

FIG. 4C shows the instrument in the first configuration and FIG. 4Ashows the instrument in the second configuration, as discussed above.

FIG. 5 is a perspective view of a dielectric cylinder used to model thecylindrical cap that forms part of the first electrode of anelectrosurgical instrument described above. It has been found that arounded cylinder having a diameter of around 2 mm and a length of 6.7 mmgives a good match into liver tissue for the microwave power at 5.8 GHz,and therefore is useful for the efficient delivery of energy in the deepcoagulation mode (i.e. the second configuration). As shown in FIGS. 6Ato 6C, the heating produced by the non-ionising radiation emitted fromthis structure is over a very small region about 1 mm radius centred onthe end of the inner conductor. FIGS. 6A and 6B show the inner conductorterminating at a flat surface with sharp edges. The fields are very highat the sharp edges. FIG. 6C shows the inner conductor terminating in adome (e.g. hemisphere), which causes the fields to be more even.

FIGS. 7A and 7B show a plot of the return loss for the structures inFIGS. 6C and 6B respectively. In general they demonstrate a good matchinto tissue around the frequency used for the microwave signal in thisembodiment (5.8 GHz). FIG. 7A shows that a hemispherical end on theinner conductor lowers the matched frequency, but this can be easilyadjusted by shortening the length of the cap.

FIGS. 8A and 8B are microwave field simulations of a cylindrical capterminating at the distal end of Sucoform 86 microwave cable from Huber& Suhner or the like (i.e. a 2.2 mm diameter cable) into blood and livertissue respectively. In this arrangement, the material used for thecylindrical cap is PEEK, and the length of the cylindrical sectionbefore the hemisphere was 3 mm. Thus, the cap (e.g. made of PEEK) has adiameter of 2 to 2.1 mm and a total length of 4 to 4.1 mm. In thisarrangement, the dome at the end of the inner conductor is modelled witha 1 mm diameter. Again the heating from such structure is localisedaround the distal tip.

FIGS. 9A and 9B show a plot of the return loss for the structures inFIGS. 8A and 8B respectively. The losses at the frequency of interesthere (around 5.8 GHz) are acceptable.

FIG. 10 is a microwave field simulation of a cylindrical cap terminatingat the distal end of Sucoform 47 microwave cable from Huber & Suhner orthe like (i.e. a 1.2 mm diameter cable) into liver tissue. In thisarrangement, the material used for the cylindrical cap is also PEEK, andthe length of the cylindrical section before the hemisphere was also 3mm. However, the diameter of the cap in this arrangement is 1.2 mm andtherefore has a total length of about 3.6 mm. In this arrangement, thedome at the end of the inner conductor is modelled with a 0.5 mmdiameter.

FIGS. 11A and 11B show a plot of the return loss for the structures ofFIG. 10 into blood and liver tissue respectively. Again, the losses atthe frequency of interest here (around 5.8 GHz) are acceptable.

FIGS. 12A and 12B show a schematic cross-sectional view through anelectrosurgical instrument 500 that is an embodiment of the invention,which utilises the microwave emitting structures discussed above withreference to FIGS. 6 to 11.

FIG. 12A shows the electrosurgical instrument 500 in a firstconfiguration that is suitable for delivering a plasma at the distalend. The instrument 500 is cylindrical, and sized to fit down theinstrument channel of a scoping device, e.g. an endoscope. Theinstrument comprises a coaxial cable 502 having an inner conductor 504and an outer conductor 506 separated from the inner conductor 504 by adielectric material 508. The outer conductor 506 is exposed around atthe outside surface of the coaxial cable 502. At the distal end of thecoaxial cable 502, the inner conductor 504 extend beyond the outerconductor 506 and its surrounding by a dielectric cap 510, e.g. made ofPEEK or the like. The cap 510 is a cylinder having substantially thesame diameter as the coaxial cable 502. The distal end of the cap 510forms a rounded, e.g. hemispherical dome. The inner conductor 504terminates at its distal end is a rounded tip 512 which projects beyondthe end of the cap 510.

The coaxial cable 502 is mounted within a sleeve 514, which preferablyincludes internal braids (not shown) to impart strength. There is anannular gap 516 between the inner surface of the sleeve 514 and theouter surface of the coaxial cable 502 (i.e. the exposed outerconductor) which forms a gas flow path for conveying gas introduces atthe proximal end of the sleeve 514 to the distal end.

A conductive terminal tube 518 is mounted at the distal end of thesleeve 514. For example, the conductive terminal tube 518 may be weldedto the sleeve 514. In the configuration shown in FIG. 12A, the roundedtip 512 of the inner conductor 504 forms a first electrode and theconductive terminal tube 518 forms a second electrode. An electric fieldfor striking a plasma in the gas flowing from the annular gap 516 isformed between the first electrode and second electrode by applyingsuitable energy (e.g. RF and/or microwave frequency energy) to thecoaxial cable, as explained above.

The conductive terminal tube 518 is electrically connected to the outerconductor 506 of the coaxial cable 502 by a plurality of radiallyprojecting bumps 520 on the inner surface of the conductive terminaltube 518. There may be two, three, four or more bumps 520 spaced fromone another around the inner circumference of the conductive terminaltube 518. Spacing the bumps in this manner permits the gas to flow past.

An insulating liner 522 is mounted around the inside surface of theconductive terminal tube 518 along a distal length thereof. Theinsulating liner 522 may be made of polyimide or the like. The purposeof the liner 522 is to provide a suitable dielectric barrier between thefirst electrode and second electrode to ensure that the applied RFand/or microwave frequency energy results in an electric field with highvoltage for striking the plasma. There is a small gap between the liner522 and the cap 510 to permit the gas to flow past.

FIG. 12B shows the electrosurgical instrument 500 in a secondconfiguration that is suitable for delivering non-ionising microwavefrequency energy at its distal end. In this configuration, the cap 510extends out of the conductive terminal tube 518, where it forms amonopolar microwave antenna as discussed above.

To transform the instrument 500 between the first configuration and thesecond configuration, the coaxial cable 502 slides axially relative tothe sleeve 514. The sliding operation may be effected by a physicalslider switch mounted on a proximal handpiece of the instrument, whereit may be operated by the surgeon.

FIG. 13 shows a perspective view of a handpiece 600 that may be usedwith or form part of the electrosurgical instrument that is anembodiment of the invention. The handpiece comprises a housing 602 orshell for surrounding and protecting the inner components. The housinghas a proximal port 604 at its back end for connecting to a coaxialcable to receive RF and/or microwave frequency energy from anelectrosurgical generator (not shown). In a middle portion of thehousing 602 there is a slider switch 606 for changing the configurationat the distal end of the instrument. On an opposite side of the housingfrom the slider switch 606 there is a gas receiving port 608 forattaching to a suitable gas feed pipe (not shown). At the distal end ofthe housing 602 there is a flexible nozzle 610 which acts as aprotective guide for the sleeve 612 that conveys the gas and energy tothe treatment location.

FIG. 14 shows a cross-sectional view of the inner components of thehousing 602. A coaxial cable 614 extends through the housing from theproximal port 604. A collar 616, e.g. of stainless steel is mounted on(e.g. soldered to) the coaxial cable 614 at a proximal end thereof. Theslider switch 606 is attached to the collar 616 via a grub screw 618.This arrangement ensures that the slider switch 606 can be securelyattached to the coaxial cable without damaging it.

The coaxial cable 614 is received in a first input port of a Y-shapedjunction 620. The second input port of the Y-shaped junction 620 isconnected to the gas receiving port 608. Gas introduced into theY-shaped junction 620 is prevented from escaping through the first inputport by a suitable seal 622.

The coaxial cable 614 extends through the Y-shaped junction 620 andexits it at an output port. A proximal end of the sleeve 612 is secured(e.g. adhered) to the output port of the Y-shaped junction 620, where itreceives both gas from the gas receiving port 608 and the coaxial cable.In use, the slider switch 606 is movable relative to the housing 602 toextend and retract the coaxial cable 614 within the sleeve 612. Themovement range of the slider switch may be 20 mm.

The invention claimed is:
 1. An electrosurgical instrument comprising:an elongate probe comprising a coaxial cable for conveyingradiofrequency (RF) and microwave frequency electromagnetic (EM) energy,and a probe tip connected at a distal end of the coaxial cable forreceiving the RF and microwave energy separately or simultaneously fromthe coaxial cable; and a gas passage for conveying gas through theelongate probe to the probe tip, wherein the coaxial cable comprises aninner conductor, an outer conductor and a dielectric material separatingthe inner conductor from the outer conductor, wherein the probe tipcomprising a first electrode connected to the inner conductor of thecoaxial cable and a second electrode connected to the outer conductor ofthe coaxial cable, wherein the first electrode and second electrode arecoaxial with each other, and wherein the first electrode and secondelectrode are arranged to: produce an electric field from the receivedRF EM energy across a flow path of gas received from the gas passage inorder to strike a plasma, and deliver the received microwave EM energyto sustain the plasma after it is struck.
 2. An electrosurgicalinstrument according to claim 1, wherein the elongate probe comprises asleeve surrounding the coaxial cable, the gas passage being a spacebetween an inside surface of the sleeve and an outside surface of thecoaxial cable.
 3. An electrosurgical instrument according to claim 2,wherein the second electrode comprises a conductive terminal tubemounted on a distal end of the sleeve, wherein the conductive terminaltube includes one or more radially projecting bumps on its inner surfacefor contacting the outer conductor of the coaxial cable.
 4. Anelectrosurgical instrument according to claim 3, wherein the conductiveterminal tube has an insulating liner around its inner surface, whereinthe liner is located distally to the one or more radially projectingbumps.
 5. An electrosurgical instrument according to claim 1, whereinthe outer conductor of the coaxial cable is connected to the secondelectrode by a gas permeable conductive structure that permits gas toflow through it.
 6. An electrosurgical instrument according to claim 5,wherein the gas permeable conductive structure is any one of: aconductive mesh; a cage of radially extending conductive wires orsprings; and a plurality of circumferentially spaced radially protrudingdents.
 7. An electrosurgical instrument according to claim 5, whereinthe gas permeable conductive structure is soldered or crimped to thesecond electrode.
 8. An electrosurgical instrument according to claim 1,wherein the elongate probe is insertable through an instrument channelof an endoscope.
 9. An electrosurgical instrument according to claim 1configured for use in a NOTES procedure.
 10. Electrosurgical apparatusfor performing coagulation comprising: a radiofrequency (RF) signalgenerator for generating RF electromagnetic (EM) energy having a firstfrequency; a microwave signal generator for generating microwave EMenergy having a second frequency that is higher than the firstfrequency; an electrosurgical instrument according to claim 1 connectedto receive the RF EM energy and the microwave EM energy; a feedstructure for conveying the RF EM energy and the microwave EM energy tothe elongate probe, the feed structure comprising an RF channel forconnecting the elongate probe to the RF signal generator, and amicrowave channel for connecting the elongate probe to the microwavesignal generator, a gas feed connected to supply gas to electrosurgicalinstrument, wherein the apparatus is operable in a surface coagulationmode whereby the RF EM energy delivered to the probe tip is arranged tostrike a gas plasma between the first and second electrodes, and themicrowave EM energy is arranged to sustain the plasma after it has beenstruck.
 11. Electrosurgical apparatus according to claim 10 comprising astrike signal generation circuit arranged to cause a pulse of RF EMenergy to be delivered to the elongate probe to generate the electricfield across the flow path for striking the plasma, wherein the strikesignal generation circuit includes control circuitry arranged to use adetectable characteristic of a pulse of microwave EM energy on themicrowave channel to trigger generation of the pulse of RF EM energy.12. Electrosurgical apparatus according to claim 10 comprising: amicrowave signal detector for sampling forward and reflected power onthe microwave channel and generating therefrom a microwave detectionsignal indicative of the microwave EM energy delivered by the elongateprobe; and a controller in communication with the microwave signaldetector to receive the microwave detection signal, wherein thecontroller is operable to select an energy delivery profile for themicrowave EM energy, the energy delivery profile for the microwave EMenergy being for coagulation of tissue, wherein the controller comprisesa digital microprocessor programmed to output a microwave control signalfor the microwave signal generator, the microwave control signal beingfor setting the energy delivery profile for the microwave EM energy, andwherein the controller is arranged to determine a state for themicrowave control signal based on the received microwave detectionsignal.